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  • 1
    Electronic Resource
    Electronic Resource
    Anti-planetward auroral electron beams at Saturn (2006)
    [s.l.] : Nature Publishing Group
    Nature 439 (2006), S. 699-702 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Strong discrete aurorae on Earth are excited by electrons, which are accelerated along magnetic field lines towards the planet. Surprisingly, electrons accelerated in the opposite direction have been recently observed. The mechanisms and significance of this anti-earthward acceleration are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04401
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  • 2
    Electronic Resource
    Electronic Resource
    The dynamic cusp at low altitudes: a case study utilizing Viking, DMSP-F7, and Sondrestrom incoherent scatter radar observations (1994)
    Springer
    Annales geophysicae 12 (1994), S. 1144-1157 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Coincident multi-instrument magnetospheric and ionospheric observations have made it possible to determine the position of the ionospheric footprint of the magnetospheric cusp and to monitor its evolution over time. The data used include charged particle and magnetic field measurements from the Earth-orbiting Viking and DMSP-F7 satellites, electric field measurements from Viking, interplanetary magnetic field and plasma data from IMP-8, and Sondrestrom incoherent scatter radar observations of the ionospheric plasma density, temperature, and convection. Viking detected cusp precipitation poleward of 75.5○ invariant latitude. The ionospheric response to the observed electron precipitation was simulated using an auroral model. It predicts enhanced plasma density and elevated electron temperature in the upper E- and F-regions. Sondrestrom radar observations are in agreement with the predictions. The radar detected a cusp signature on each of five consecutive antenna elevation scans covering 1.2 h local time. The cusp appeared to be about 2○ invariant latitude wide, and its ionospheric footprint shifted equatorward by nearly 2○ during this time, possibly influenced by an overall decrease in the IMF Bz component. The radar plasma drift data and the Viking magnetic and electric field data suggest that the cusp was associated with a continuous, rather than a patchy, merging between the IMF and the geomagnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-1144-7
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  • 3
    Electronic Resource
    Electronic Resource
    Dayside isotropic precipitation of energetic protons (1997)
    Springer
    Annales geophysicae 15 (1997), S. 1233-1245 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Recently it has been shown that isotropic precipitation of energetic protons on the nightside is caused by a non-adiabatic effect, namely pitch-angle scattering of protons in curved magnetic field lines of the tail current sheet. Here we address the origin of isotropic proton precipitation on the dayside. Computations of proton scattering regions in the magnetopheric models T87, T89 and T95 reveal two regions which contribute to the isotropic precipitation. The first is the region of weak magnetic field in the outer cusp which provides the 1–2° wide isotropic precipitation on closed field lines in a ∼2–3 hour wide MLT sector centered on noon. A second zone is formed by the scattering on the closed field lines which cross the nightside equatorial region near the magnetopause which provides isotropic precipitation starting ≈1.5–2 h MLT from noon and which joins smoothly the precipitation coming from the tail current sheet. We also analyzed the isotropic proton precipitation using observations of NOAA low altitude polar spacecraft. We find that isotropic precipitation of 〉30 to 〉 80 keV protons continues around noon forming the continuous oval-shaped region of isotropic precipitation. Part of this region lies on open field lines in the region of cusp-like or mantle precipitation, its equatorward part is observed on closed field lines. Near noon it extends ∼1–2° below the sharp boundary of solar electron fluxes (proxy of the open/closed field line boundary) and equatorward of the cusp-like auroral precipitation. The observed energy dispersion of its equatorward boundary (isotropic boundary) agrees with model predictions of expected particle scattering in the regions of weak and highly curved magnetic field. We also found some disagreement with model computations. We did not observe the predicted split of the isotropic precipitation region into separate nightside and dayside isotropic zones. Also, the oval-like shape of the isotropic boundary has a symmetry line in 10–12 MLT sector, which with increasing activity rotates toward dawn while the latitude of isotropic boundary is decreasing. Our conclusion is that for both dayside and nightside the isotropic boundary location is basically controlled by the magnetospheric magnetic field, and therefore the isotropic boundaries can be used as a tool to probe the magnetospheric configuration in different external conditions and at different activity levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-1233-5
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  • 4
    Electronic Resource
    Electronic Resource
    A satellite study of dayside auroral conjugacy (1995)
    Springer
    Annales geophysicae 13 (1995), S. 1134-1143 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A study of dayside auroral conjugacy has been done using the cleft/boundary layer auroral particle boundaries observed by the DMSP-F7 satellite in the southern hemisphere and the global UV auroral images taken by the Viking spacecraft in the northern hemisphere. The 22 events have been studied on the basis of an internal IGRF 1985 magnetic field; it is shown that there is a displacement of up to 4° in latitude from the conjugate points with the northern aurora appearing to be located poleward of the conjugate point. No local time dependence of the north-south auroral location difference was seen. The use of a more realistic magnetic field model for tracing field lines which incorporates the dipole tilt angle and Kp index, the Tsyganenko 1987 long model plus the IGRF 1985 internal magnetic field model, appears to organize the data better. Although with this external plus internal model some tracings did not close in the opposite hemisphere, 70% of those that did indicated satisfactory conjugacy. The study shows that the degree of auroral conjugacy is dependent upon the accuracy of the magnetic field model used to trace to the conjugate point, especially in the dayside region where the field lines can either go to the dayside magnetopause near the subsolar point or sweep all the way back to the flanks of the magnetotail. Also the discrepancy in the latitude of northern and southern aurora can be partially explained by the displacement of the neutral sheet (source region of the aurora) by the dipole tilt effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-1134-4
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    Paper (German National Licenses)
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